In minimally invasive medical procedures a needle, laser or other surgical tool is inserted into a patient's body. Minimally invasive procedures are performed for several reasons, such as taking tissue samplings, abscess drainage, laser ablation, screw insertion, teeth implantation etc. One common minimally invasive procedure is the biopsy procedure which involves guiding a needle along an anatomical trajectory to an anatomical location in the patient's body. For example, a biopsy needle may be used to take a sample from a lesion in the patient's body. These minimally invasive procedures are becoming more common because they serve as alternatives to full scale surgery.
Nevertheless, biopsy procedures are painful medical procedures. In addition, inaccurate movements could cause severe damage to healthy organs of the patient, for example, puncturing a main blood vessel.
In order to accurately perform the biopsy procedure, a biopsy needle trajectory is commonly planned before insertion of the needle. The planning is usually performed on images acquired by imaging systems such as computed tomography (CT), ultrasonography and magnetic resonance imaging (MRI). The needle trajectory is chosen so as to minimize unnecessary damage to tissue in the patient's body.
But although exact planning is feasible, implementing the planned trajectory is not simple. Ordinarily, the surgeon sees only the patient's skin. In some cases internal landmarks such as the bone structure of the patient can help orient the surgeon, but in most cases, especially in abdominal biopsies, such landmarks do not exist. Furthermore, the patient's body can move and the orientation of his inner organs can change, between the acquisition of the image and the invasive procedure. In longer procedures or if there is a considerably delay between image acquisition and the biopsy procedure, there is a high probability that the trajectory as planned (on the image) will not match the anatomical trajectory (as performed).
As a result, in many biopsy procedures, multiple trials of needle insertion are necessary to position the needle at a desired anatomical location within the patient.
Several solutions to precise biopsy needle guiding have been developed. One solution is a use of rigid guides, along which a biopsy needle is guided into the body. These rigid guides provide precise positioning of the biopsy needle but usually have a limited range of angles at which a needle can be inserted. In some head procedures a stereotactic frame is used to guide a needle into the patient's head. This frame is cumbersome, blocks the view of the surgeon and may also interfere with the surgeon's movements. Stereotactic frames are also used for spinal procedures.
Another solution uses tracking devices. In this method either a relatively large brace-like structure or three fiducial implants are temporarily attached to the patient's body, before imaging. In the resulting image, the fiduciary marks or the frame are used to generate an external reference frame, to which the planned needle trajectory is registered. Such a system is described for example in U.S. Pat. No. 5,142,930, whose disclosure is incorporated herein by reference. The '930 patent describes a system comprising an articulated arm, in which positional encoders are used to determine the location of a tool mounted on the arm. Various invasive tools may be attached to the arm. The position of the distal tip of the invasive tool is continuously calculated and transmitted to a computer. The computer controls an imaging apparatus to acquire images, including a slice which contains the tip of the invasive tool. In this method the images are real-time images. In another known method the computer displays previously acquired images based on the tool position.
U.S. Pat. No. 4,651,732, whose disclosure is incorporated herein by reference describes another method in which a light beam marks the trajectory chosen for a biopsy needle. While performing the biopsy the surgeon guides the needle into the patient's body by following the light beam.